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As this happens, microtubules invade the nuclear space. This is called open mitosis, and it occurs in some multicellular organisms. Fungi and some protists, such as algae or trichomonads, undergo a variation called closed mitosis where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope. [45] [46]
Fungi and some algae can also utilize true asexual spore formation, which involves mitosis giving rise to reproductive cells called mitospores that develop into a new organism after dispersal. This method of reproduction is found for example in conidial fungi and the red algae Polysiphonia, and involves sporogenesis without meiosis. Thus the ...
The term "plants" is taken here to mean the Archaeplastida, i.e. the glaucophytes, red and green algae and land plants. Alternation of generations occurs in almost all multicellular red and green algae, both freshwater forms (such as Cladophora) and seaweeds (such as Ulva). In most, the generations are homomorphic (isomorphic) and free-living.
During mitosis the algae is transferred to only one of the daughter cells, while the other cell restarts the cycle. In 1966, biologist Kwang W. Jeon found that a lab strain of Amoeba proteus had been infected by bacteria that lived inside the cytoplasmic vacuoles. [74] This infection killed almost all of the infected protists.
Mitochondrial fission occurs frequently within the cell, even when the cell is not actively undergoing mitosis, and is necessary to regulate the cell's metabolism. [15] All chloroplasts and some mitochondria (not in animals), both organelles derived from endosymbiosis of bacteria, also use FtsZ in a bacteria-like fashion. [5] [16]
[20] [21] The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or hydrogenosomes. [22] Another engulfment of cyanobacterial -like organisms led to the formation of chloroplasts in algae and plants.
Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped body called the nucleoid. [66] The nucleoid contains the chromosome with its associated proteins and RNA.
Hydrogen hypothesis, the theory that mitochondria were acquired by hydrogen-dependent archaea, their endosymbionts being facultatively anaerobic bacteria; Kleptoplasty, the sequestering of plastids from ingested algae; Mixotricha paradoxa, which itself is a symbiont, contains numerous endosymbiotic bacteria